It has taken a while but the project is now finished. The final result is as described in the previous articles with the exception of no longer using an HDMI receiver. I am now using a Behringer FCA610 usb sound card.
The boxes are of simple construction, 18mm Baltic birch front panels and 18mm mdf for the rest. The mid uses a tube for its volume, and the horn enclosure is entirely cosmetic. The bass box was based on the plans of the JBL 4345, I used the same bracing and external dimensions. The fronts were painted with a textured cab paint, and the rest was covered with brown paper, ala paper bag flooring. Each driver was measured individually and linear filters made with Rephase with phase correction. While not an ideal measurement as taken in room with a longer window to include the bass response, the resulting response is flat with linear phase. And finally the in room response at listening position: With the speakers toed in at 45 degrees, the controlled dispersion of the SEOS horn does an outstanding job of reducing room interaction.